Aqueous solutions containing surfactants and, optionally, so-called builders, such as alkali hydroxides, alkali carbonates, silicates and phosphates, complexing agents and organic or inorganic corrosion inhibitors, are used for cleaning and degreasing on an industrial scale, more particularly, for cleaning and degreasing metal surfaces. In practical application, these cleaning solutions become contaminated by mineral oil and/or natural oils to which emulsifiers, corrosion inhibitors and other oil additives may be added. These impurities, which are emulsified by any emulsifiers present in the oil and by the surfactants of the cleaning agent in the solution, weaken the effectiveness of the aqueous solutions and, ultimately, render them ineffectual. The solutions then have to be renewed.
Before the used solutions are run off into drains, they have to be freed from oil and, if they are alkaline, neutralized in accordance with applicable government regulations. Neutralization alone is generally not sufficient to remove all the oils. Accordingly, the emulsion has to be broken. This may be done by various methods, for example by reducing the pH-value to approximately 1, by increasing the salt content of the solution, or by adding flocculating agents, such as aluminium or iron salts, in the acidic range, followed by re-neutralization.
The ingredients of the cleaning solution are lost when the cleaning solutions are run off into the drains and also at the effluent treatment stage. Accordingly, it is advantageous to regenerate spent cleaning solutions to enable them to be reused and to prolong the useful life of the baths.
Aqueous degreasing solutions can be regenerated by ultrafiltration, by centrifugal separators, and by annular chamber deoilers. Ultrafiltration is, above all, expensive and relies heavily on machinery. With centrifugal separators and annular chamber deoilers, however, it is only possible to regenerate degreasing solutions in which the oils and impurities are not in the form of stable emulsions. In many instances, oils and drawing compounds which contain anionic emulsifiers and which, without the assistance of the cleaning agent, form stable emulsions that cannot be demulsified by physical processes, are washed off and entrained into the bath solution.
Chemical demulsification processes, i.e. processes in which emulsions are separated into their components, are known for example from U.S. Pat. No. 4,029,708 which describes linear, surface-active anionic or acid-neutralized polymers which are formed by polymerization of substituted oligoamines, such as for example ethylene diamine or diethylene triamine, and bifunctional reagents, such as for example epichlorhydrin or 1,4-dichloro-2-butene. However, emulsions containing alkalis and/or anionic surfactants cannot be demulsified by these polymers.
According to British Pat. No. 1,509,042, processes for removing oils and solvents from effluents by means of mixtures of ionic starch derivatives and flocculants of opposite ionity also result in the separation of organic materials from aqueous solutions. However, if oils or organic solvents are stably emulsified in the effluents, the effect of the described mixtures of starch derivatives and flocculants is greatly reduced or even eliminated altogether because the adsorptive addition of the starch derivatives onto the organic effluent constituents to be removed and subsequent coagulation by the flocculants disclosed in the above patent is only possible when the organic substances are "freely" suspended in the water and not surrounded by emulsifier molecules. Accordingly, before separation from the contaminated waters can take place, any emulsions present first have to be broken.
In most cases, however, aqueous solutions for cleaning and degreasing metal surfaces on an industrial scale not only have neutral to alkaline pH-values, but are also contaminated by emulsified mineral and/or natural oils, particularly by oils and fats which, following the addition of appropriate emulsifiers, have a self-emulsifing effect. The emulsifiers are predominantly anionic in character. In addition, the cleaning and degreasing solutions frequently contain alkalis, such as alkali metal hydroxides, alkali metal carbonates and alkali metal borates, silicates and phosphates, and also complexing agents, such as complexing phosphonic acids or phosphonocarboxylic acids, particularly 1-hydroxy alkane-1,1-diphosphonic acid, 1-aminoalkane-1, 1-diphosphonic acid or aminotrimethylene triphosphonic acid or their alkali metal salts and, frequently, inorganic and organic corrosion inhibitors.
Hitherto, it has not been possible for contaminated cleaning solutions such as these to be readily freed from oils or other organic contaminants.